JS基础

javascript基础语言与其他语言大差不差，看代码理解即可。复习笔记

变量与数据类型

变量名要见名知意变量名可以是字母、下划线、$，还有数字；但是不能以数字开头小写字母开头，多个单词，第二个单词首字母大写（驼峰命名）

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Document</title>
</head>
<body><script>//var变量声明var s = "hello world",s2 = "hello";console.log(s);console.log(s2);console.log(2);</script><!-- 命名规范 --><!-- 变量名要见名知意
变量名可以是字母、下划线、$，还有数字；
但是不能以数字开头小写字母开头，
多个单词，第二个单词首字母大写（驼峰命名） -->
</body>
</html>

表达式与运算符

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Document</title>
</head>
<body><script>//字面量，例如“hello world”//运算符,和C那一套基本一样console.log("hello" + "world");//比较运算符console.log(20 == "20");//trueconsole.log(20 === "20")//最佳，不会进行类型转换//逻辑运算符也是和C一样</script>
</body>
</html>

条件语句

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Document</title>
</head>
<body><script>var num1 = 10, num2 = 20;var result = num1 + num2;console.log(result);if(result === 30){ console.log("你好");}//switch语句switch(result){case 30 : console.log("correct");break;default:console.log("wrong");}</script>
</body>
</html>

循环语句

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Document</title>
</head>
<body><script>//和C一模一样，不详细写了for(var i = 1; i <= 100;i++){console.log(i);console.log("你好");}</script>
</body>
</html>

函数基础

记得格式，还有回调函数！

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><meta name="viewport" content="width=, initial-scale=1.0"><title>Document</title>
</head>
<body><script>//函数格式function fun(x){var result = 3*x + 4;// console.log(result);return result;}console.log(fun(3));</script>
</body>
</html>

数组

数组稍微和C有点出入，有一些内置的方法记得使用。

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Document</title>
</head>
<body><script>//可存储不同数据类型的数var list = ["a","b",3];//new 构造函数// var list = new Array("a","b","c");console.log(list);//索引访问console.log(list[0]);//方法console.log(list.length);//遍历数组for(var i = 0; i < list.length;i++)console.log(list[i]);//map方法遍历list.map(function(value,index){console.log("第"+(index+1) + "个元素是"+value);});//push方法list.push("f");console.log(list);//sort排序list.sort();console.log(list);//过滤器,利用回调函数var mewList = list.filter(function(item){if(item >= 3){return item;}})console.log(mewList);//连接成字符串var str = list.join("-");//split方法，join逆向console.log(str);var lis = str.split("-");console.log(lis);//数据获取,字典var newL = [{name : "小米",age :2,sex:"男"},]console.log(newL[0].name);</script>
</body>
</html>

对象

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Document</title>
</head>
<body><script>//属性的集合var cat = {name : "喵喵",age : 2,sayName:function(){console.log("我是" + cat.name);}}//值的获取console.log(cat.name);console.log(cat["age"]);//初始化对象为空var student = null;var v;console.log(v);//undefinedcat.sayName();</script></body>
</html>

常用内置对象

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Document</title>
</head>
<body><script>//mathvar num = 3.14;//向下取整var result = Math.floor(num);console.log(result);//随机数var ret = Math.random();console.log(ret);//绝对值var rett = Math.abs(ret);//开方var rett = Math.sqrt(ret);//乘方var rettt = Math.pow(ret,4); //Date对象var date = new Date();console.log(date);//获取年var year = date.getFullYear();console.log(year);//时间戳console.log(date.getTime());//计时器方法var n = 0;setInterval(function( ){//Date对象var date = new Date();console.log(date);//每一千毫秒输出一次},1000)</script>
</body>
</html>